The present invention relates to lighting, and particularly to a lamp, e.g., an automotive lamp having a lens in which a thermally transferred decal provides shielding against radio noise from the light source of the lamp. The invention also relates to the lens and to methods for producing the lens and the lamp assembly.
Automotive lamps generally include a housing having a reflective coating, a light source mounted within the housing, and a lens sealed to the housing rim. The housing may be fabricated from a metal or a rigid polymeric material coated with a metal to provide the required reflective coating, while the lens is generally molded from polycarbonate or acrylic polymers. When the light source, however, emits significant electromagnetic radiation outside the visible frequency, this assembly may further require means to shield nearby electronic devices from the unwanted radiation. The terms "electromagnetic interference" (EMI), "radio frequency interference" (RF), or "radio noise" are most commonly used to describe extraneous radiation that interferes with operation of electronic devices. In an automobile, these devices may include radios, on-board computer controls, and mobile communication devices. Interference from the light source radiation may also cause problems in devices near the automobile or associated with passengers therewithin, e.g., pacemakers, radios, computers, and communication devices. Most EMI problems with these devices are limited to frequencies between 1 KHz and 10 GHz. For convenience, the term EMI is used herein to refer generally to such unwanted radio and audio frequencies.
One type of prior art EMI shielding of automotive lamps combines the conductive properties of the housing or housing metallic coating with a wire mesh screen covering the area enclosed by the lens, both the housing and the screen being electrically grounded. This wire mesh is difficult to work with during product assembly because it is not easily processed by automatic assembly equipment. It also adds potential for failure of the bond sealing the lens to the housing. Further, it is difficult and costly to form such wire mesh screens into the shapes required for non-planar lenses, e.g., those having recurved or other complex lens shapes.
Another type of prior art EMI shielding of a lamp involves an evaporative metal coating on the lens. This is a costly and complex process requiring precise control of the thickness of the coating. The process also results in significant loss of light emitted by the lamp.
Accordingly, it is an object of the present invention to provide an EMI shielding lamp which overcomes the disadvantages of the prior art.
It is another object of the invention to provide an EMI shielding lamp lens which is readily and economically processed and assembled by automatic equipment.
It is yet another object of the invention to provide a lamp lens having an EMI shielding means included as an integral part of the lens.
It is still another object of the invention to provide radio noise shielding on planar andnon-planar lamp lenses, including those having recurved or other complex lens shapes.
Further objects of the invention are to provide straightforward and economical methods for producing a unitary radio noise shielding lamp lens and for producing a lamp assembly having a unitary radio noise shielding lens.